This invention relates to the field of High Voltage Direct Current transmission line apparatus connecting two alternating current systems and more specifically to a method and apparatus to control or regulate the system-synchronous converters of a HVDC system.
In such a HVDC system the converter of one station, A, impresses the HVDC transmission current while the converter of the other station, B, determines the HVDC transmission voltage. The operation of the current impressing station, as will be explained in greater detail below, is a function of the HVDC voltage produced by the other station used as a fault indication quantity, whereas the operation of the voltage-determining converter must take into account the impressed current in determining its commutation times.
Each converter thus requires information regarding the operating status of the corresponding other converter. For long distance transmission in addition this mutual interlinkage of the converters is further characterized by having a lag time, namely the travel time of the HVDC, so that stable operation is hard to attain, particularly if the mutual information transmittal is handled by remote control lines having additional transmittal and processing times.
The purpose of this invention is to provide the information required in the simplest possible fashion to assure stable operation and to process the information in the converter stations.